To block or mute certain words on Twitter (now called X), use the "Muted words" feature in the settings. Here are the steps:

1. Open the Twitter (X) app or website and log in.
2. On the app, tap your profile picture or the sidebar menu and select "Settings and privacy."
3. Go to "Privacy and safety."
4. Tap "Mute and block," then select "Muted words."
5. Click or tap "Add" (plus icon) to enter words, phrases, or hashtags you want to block or mute.
6. Choose where to mute these words (Home timeline, Notifications, or both).
7. Set the duration for muting (from 24 hours to indefinitely).
8. Save the changes.

After you mute these words, tweets containing them won't appear in your timeline or notifications, helping you avoid unwanted content. Note that muting words doesn't block the users themselves, only the content containing those words.

This feature allows you to tailor your Twitter experience by filtering out specific words or topics you prefer not to see.